As an electro-photographic type color laser printer, a tandem type color laser printer is known in which a plurality of photosensitive drums are juxtaposed with each other for the color of yellow, magenta, cyan and black.
In a conventional tandem type color laser printer, a belt unit having an endless belt is provided and a plurality of photosensitive drums juxtaposed with each other is positioned above and in contact with the endless belt.
According to the conventional color printer, each process cartridge accommodating each photosensitive drum is detachably attached to a cartridge tray. The cartridge tray is inserted into an interior of a main casing of the printer while a door is opened, and is positioned above the endless belt. Then, a pressure member positioned above each process cartridge is pivotally moved downward in interlocking relation to the closing movement of the door. The main casing has a positioning portion for positioning the process cartridges relative to the endless belt and the main casing as a result of pressure application from the pressure members. Thus, each pressure member presses each process cartridge downward whereupon each photosensitive drum is brought into contact with the endless belt, and positioning of each photosensitive drum with respect to the endless belt and the main casing is attained.
Japanese Patent Application Publication 2010-244071 discloses a tandem type color printer in which photosensitive drums are positioned below an intermediate transfer belt in a form of an endless belt, and each photosensitive drum is configured to contact the intermediate transfer belt.
According to the color printer disclosed in '071 publication, a plurality of process cartridges each accommodating each photosensitive drum are positioned below the belt unit. Each photosensitive drum has an upper peripheral part exposed to the intermediate transfer belt through each process cartridge. Thus, each photosensitive drum is in contact with the intermediate transfer belt from below.